arXiv subjects

Hiori Kino

Publications and source records attributed to Hiori Kino.

29 records · Page 2Linked to original sources

arXiv2015

Quasiparticle self-consistent GW study of cuprates: electronic structure, model parameters, and the two-band theory for Tc

Despite decades of progress, an understanding of unconventional superconductivity still remains elusive. An important open question is about the material dependence of the superconducting properties. Using the quasiparticle self-consistent GW method, we re-examine the electronic structure of copper oxide high-Tc materials. We show that QSGW captures several important features, distinctive from the conventional LDA results. The energy level splitting between dx2-y2 and d3z2-r2 is significantly enlarged and the van Hove singularity point is lowered. The calculated results compare better than LDA with recent experimental results from resonant inelastic xray scattering and angle resolved photoemission experiments. This agreement with the experiments supports the previously suggested two-band theory for the material dependence of the superconducting transition temperature, Tc.

cond-mat.str-el↗

arXiv2014

Formulation of the augmented plane-wave and muffin-tin orbital method

A mixed basis all-electron full-potential method, which uses two kinds of augmented waves, the augmented plane waves and the muffin-tin orbitals simultaneously, in addition to the local orbitals, was proposed by Kotani and van Schilfgaarde in Phys. Rev. B81, 125117(2010). We named it the PMT method. In this paper, this mixed basis method is reformulated on the basis of a new formalism named as the 3-component formalism, which is a mathematically transparent version of the additive augmentation originally due to Soler and Williams in Phys. Rev. B47, 6784(1993). Atomic forces are easily derived systematically. We discuss some problems in the mixed basis method and ways to manage them. In addition, we compare the method with the PAW method on the same footing. This PMT method is the basis for our new development of the quasiparticle self-consistent $GW$ method in J.Phys.Soc.Jpn 83, 094711(2014).

cond-mat.mtrl-sci↗

arXiv2014

Quasiparticle self-consistent GW study of LaNiO$_3$ and LaNiO$_3$/LaAlO$_3$ superlattice

Using quasiparticle self-consistent $GW$ calculations we examined the electronic structure of LaNiO$_3$ and the LaNiO$_3$/LaAlO$_3$ superlattice. The effects of electron correlation in Ni-$d$ bands were reasonably well described without any {\it ad hoc} parameter and without the ambiguity related to the double-counting and downfolding issues. The effective mass is about $30\%$ enhanced compared to the GGA result. One band feature, which is believed to be essential for the cuprate-like superconductivity, is not realized and the central Fermi surface pocket does not disappear. Our result is consistent with a recent dynamical mean field calculation based on the $d$--$p$ model and in contrast to the result from a $d$-band only model.

cond-mat.str-el↗

arXiv2009

Efficient implementation of the nonequilibrium Green function method for electronic transport calculations

An efficient implementation of the nonequilibrium Green function (NEGF) method combined with the density functional theory (DFT) using localized pseudo-atomic orbitals (PAOs) is presented for electronic transport calculations of a system connected with two leads under a finite bias voltage. In the implementation, accurate and efficient methods are developed especially for evaluation of the density matrix and treatment of boundaries between the scattering region and the leads. Equilibrium and nonequilibrium contributions in the density matrix are evaluated with very high precision by a contour integration with a continued fraction representation of the Fermi-Dirac function and by a simple quadratureon the real axis with a small imaginary part, respectively. The Hartree potential is computed efficiently by a combination of the two dimensional fast Fourier transform (FFT) and a finite difference method, and the charge density near the boundaries is constructed with a careful treatment to avoid the spurious scattering at the boundaries. The efficiency of the implementation is demonstrated by rapid convergence properties of the density matrix. In addition, as an illustration, our method is applied for zigzag graphene nanoribbons, a Fe/MgO/Fe tunneling junction, and a LaMnO$_3/$SrMnO$_3$ superlattice, demonstrating its applicability to a wide variety of systems.

cond-mat.mes-hall↗

arXiv2009

Re-examination of half-metallic ferromagnetism for doped LaMnO3 in quasiparticle self-consistent $GW$ method

We apply the quasiparicle self-consistent $GW$ (\qsgw) method to a cubic virtual-crystal alloy La$_{1-x}$Ba$_x$MnO$_3$ %(LBMO) as a theoretical representative for colossal magnetoresistive perovskite manganites. The \qsgw\ predicts it as a fully-polarized half-metallic ferromagnet for a wide range of $x$ and lattice constant. Calculated density of states and dielectric functions are consistent with experiments. In contrast, the energies of calculated spin wave are very low in comparison with experiments. This is affected neither by rhombohedral deformation nor the intrinsic deficiency in the \qsgw method. Thus we ends up with a conjecture that phonons related to the Jahn-Teller distortion should hybridize with spin waves more strongly than people thought until now.

cond-mat.mtrl-sci↗

arXiv2009

Dual Spin Filter Effect in a Zigzag Graphene Nanoribbon

By first principle calculations, a dual spin filter effect under finite bias voltages is demonstrated in an antiferromagnetic junction of symmetric zigzag graphene nanoribbon (ZGNR). Unlike conventional spin filter devices using half metallic materials, the up- and down-spin electrons are unidirectionally filtered in the counter direction of the bias voltage, making the junction a dual spin filter. On the contrary, asymmetric ZGNRs do not exhibit such a spin filter effect. By analyzing Wannier functions and a tight-binding model, we clarify that an interplay between the spin polarized band structure of $π$ and $π^*$ states near the Fermi level and decoupling of the interband hopping of the two states, arising from the symmetry of the wave functions, plays a crucial role in the effect.

cond-mat.mes-hall↗

arXiv2009

Theoretical study of electronic and atomic structures of (MnO)n

We calculate the electronic and atomic structure of (MnO)n (n=1-4) using the HF exchange, VWN, PBE and B3LYP exchange-correlation functionals. We also perform diffusion Monte Carlo calculation to evaluate more accurate energies. We ompare these results and discuss the accuracy of the exchange-correlation functionals.

cond-mat.mtrl-sci↗

arXiv2006

First-Principles Study of Electronic Structure in $α$-(BEDT-TTF)$_2$I$_3$ at Ambient Pressure and with Uniaxial Strain

Within the framework of the density functional theory, we calculate the electronic structure of $α$-(BEDT-TTF)$_2$I$_3$ at 8K and room temperature at ambient pressure and with uniaxial strain along the $a$- and $b$-axes. We confirm the existence of anisotropic Dirac cone dispersion near the chemical potential. We also extract the orthogonal tight-binding parameters to analyze physical properties. An investigation of the electronic structure near the chemical potential clarifies that effects of uniaxial strain along the a-axis is different from that along the b-axis. The carrier densities show $T^2$ dependence at low temperatures, which may explain the experimental findings not only qualitatively but also quantitatively.

cond-mat.str-el↗

arXiv2003

Phase Diagram of $β'$-(BEDT-TTF)$_2$ICl$_2$ under High Pressure Based on the First-Principles Electronic Structure

We present a theoretical study on the superconductivity of $β'$-(BEDT-TTF)$_2$ICl$_2$ at $T_{\rm c}=$14.2 K under a high hydrostatic pressure recently found, which is the highest among organic superconductors. In the present work, we study an effective model using the fluctuation-exchange (FLEX) approximation based on the results of first-principles calculation. In the obtained phase diagram, the superconductivity with $d_{xy}$-like symmetry is realized next to the antiferromagnetic phase, as a result of the one-dimensional to two-dimensional crossover driven by the pressure.

cond-mat.supr-con↗

arXiv1999

Interplay between Structure and Electronic Properties in Organic Conductors

It is known that the ground states of organic conductors have a diversity reflecting the spatial arrangement of the constituent molecules within the unit cell. A systematic theoretical search for the unifying view behind such possible ground states has been made based on the Hartree-Fock mean field approximation not only to the on-site but also to intersite Coulomb interactions with special emphasis on the families of typical organic conductors (TMTCF)$_2X$ and (ET)$_2X$.

cond-mat.str-el↗

arXiv1998

Phase Diagram of Superconductivity on the Anisotropic Triangular Lattice Hubbard Model

We study the electronic states of the anisotropic triangular lattice Hubbard model at half filling, which is a simple effective model for the organic superconducting $κ$-BEDT-TTF compounds. We treat the effect of the Coulomb interaction by the fluctuation exchange (FLEX) method, and obtain the phase diagram of this model for various sets of parameters. It is shown that the d-wave superconductivity is realized in the wide region of the phase diagram, next to the antiferromagnetic states. The obtained phase diagram explains the characters of the experimental results very well.

cond-mat.supr-con↗